1. Field of the Invention
The present invention relates to a recording medium transport device that nips and transports a recording medium, and an image forming apparatus including the recording medium transport device and a printing part.
2. Background Art
Conventionally, in an apparatus for forming an image by causing ink jetted from a nozzle of an ink-jet recording head to adhere to a recording medium, the recording medium is made to intermittently move (step feeding) in a sub-scanning direction every specified length, and during the stop of the intermittent movement, a carriage on which the recording head is mounted is moved in a main scanning direction, and an image is formed in every specified area.
In that case, an upstream side transport roller pair at a transport upstream side (hereinafter simply referred to as an upstream side) in a transport direction and a downstream side transport roller pair at a transport downstream side (hereinafter simply referred to as a downstream side) are disposed at both sides of the recording head, the recording medium is nipped by both the roller pairs, and both the roller pairs are intermittently driven to move the recording medium in a sub-scanning direction. Such a structure is disclosed in JP-A-6-56298 and JP-A-6-328798.
In JP-A-6-56298, plural pinch rollers as driven rollers in the upstream side transport roller pair are attached to one pinch roller holder made of synthetic resin at suitable intervals in its longitudinal direction (direction orthogonal to the transport direction of the recording medium). The pinch roller holder is rotatably coupled to a corresponding hole part of an upper guide through a chassis (frame) by a boss part, one end of a single pinch roller spring is supported by the pinch roller holder above the boss part, the other end of the pinch roller spring is supported by a spring receive part of the upper guide, and the plural pinch rollers are pressed to the peripheral surface of a transport roller as a driving side through the pinch roller holder. Accordingly there has been a problem that a suitable pressing force cannot be applied to each of the pinch rollers.
In order to solve this problem, in JP-A-6-328798, support shafts provided to protrude at both end parts of one pinch roller holder made of synthetic resin in a longitudinal direction (direction orthogonal to the transport direction of the recording medium) are rotatably supported by a chassis (frame), and the pinch rollers are attached to the pinch roller holder at suitable intervals. Then, plural torsion coil springs are disposed to the pinch roller holder from above at suitable intervals in the direction orthogonal to a paper passing direction, and the pinch rollers are pressed to the transport roller. Besides, a slit or a notch long in the paper passing direction is formed in the pinch roller holder between the adjacent pinch rollers.